<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta http-equiv="X-UA-Compatible" content="IE=edge">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>Document</title>
</head>
<body>
 
  

 <script>
   function changeNum(a,b) {
        let temp = 0
        temp = a
        a =  b 
        b = temp
     console.log(a);
     console.log(b);     
   }
  changeNum(1,2)
 </script> 
</body>
</html>